Method for producing calcium carbonate

ABSTRACT

Calcium carbonate in the form of aragonite crystals suitable for use as a filler for papermaking to give useful properties for bulk, whiteness, opacity, wire abrasion and yield is obtained by taking advantage of the causticization step.  
     Herein disclosed is a process for producing calcium carbonate in the form of aragonite crystals which is useful as a filler for papermaking via the causticization step of the sulfate or soda pulping process, comprising adding an aqueous alkaline solution having a hydroxide ion level of 3 mol/l or less and containing 0.25 mol or less of carbonate ion per 1 mol of quick lime to quick lime and/or slaked lime at a quick lime concentration of 1-60% by weight with stirring to prepare milk of lime, and then adding green liquor to said milk of liquor at a loading rate of 0.002-0.12 g (sodium carbonate)/min/g (quick lime) to perform a causticization reaction at a temperature of 30-105° C.

FIELD OF THE INVENTION

[0001] The present invention relates to processes for producing calciumcarbonate in the form of aragonite crystals giving useful performance asa filler for papermaking and a coating pigment for papermaking via acausticization step of the sulfate or soda pulping process, and morespecifically processes for producing calcium carbonate in the form ofaragonite crystals giving useful performance as a filler for papermakingby using an aqueous alkaline solution for suspending quick lime or/andslaked lime.

PRIOR ART

[0002] Normally, printing or writing paper contains a filler for thepurpose of improving whiteness, opacity, smoothness, writingsuitability, touch, printability or other properties. These papersinclude so-called acid paper made at about pH 4.5 using talc, clay,titanium oxide or the like as a filler and so-called neutral paper madeat a neutral to weakly alkaline pH range of 7.0-8.5. In neutral paper,domestic calcium carbonate can be used as a filler in place of expensiveimported talc or clay. Recently, neutral paper has attracted attentionbecause of its longevity or other reasons, and the change to neutralpaper is advancing and will prevail because of its further manyadvantages in paper quality, costs, environmental protection or thelike.

[0003] A feature of recent demands for paper is a significant growth inthe field of leaflets, catalogs, pamphlets, direct mails or the like incommercial printing and in the field of computer-, multimedia- andfamily computer-related books reflecting the popularization ofinformation technology, magazines, comics or the like in publishing,which urges paper users to seek low-cost, low-grade and light-weightpaper.

[0004] Under growing demands for inexpensive and light-weight neutralpaper as described above, the position of calcium carbonate as a filleris very important. Calcium carbonate used as a filler in such neutralpaper includes heavy calcium carbonate obtained by mechanically dry- orwet-grinding natural limestone and precipitated calcium carbonate whichis chemically synthesized (synthetic calcium carbonate).

[0005] However, heavy calcium carbonate obtained by grinding naturallimestone by a mill such as a ball mill severely wears a plastic wireduring papermaking when it is used as filler. Moreover, normalfine-quality papers or coated papers made with such filler areinsufficient in bulk, opacity, smoothness, writing suitability, touch,printability and other properties.

[0006] The above problem becomes more serious with recent advances inweight reduction. Conventional means for improving the opacity oflight-weight printing papers were fillers having a large specificsurface area (e.g. pulverized silica, white carbon) or a high refractiveindex (e.g. titanium dioxide). These fillers improved opacity, but didnot have effective stiffness because they were unable to increase bulk(i.e. could not lower density). One possible means for increasing bulkis to increase the freeness of the pulp used, in which case theresulting paper has a high bulk and a low density but also shows aporous paper layer structure to lower air permeability and smoothness.If such a porous base paper having a low air permeability is coated witha pigment coating color, the coating color excessively penetrates thebase paper to lower various printability properties such as base papercovering properties, surface smoothness after drying, gloss beforeprinting and surface properties with even gloss.

[0007] In order to solve these problems, precipitated calcium carbonatehas been used. Known preparation processes thereof include (1) thecarbon dioxide process involving a reaction between milk of lime andcarbon dioxide obtained from the calciner of limestone or the like, (2)the calcium chloride/soda process involving a reaction between sodiumcarbonate and calcium chloride, (3) the lime/soda process involving areaction between sodium carbonate and milk of lime, etc. Among them,both processes (2) and (3) produce calcium carbonate as a by-product andare now abolished and replaced by alternative ways to their mainproducts. Moreover, the applicability of the resulting calcium carbonateto paper has been less examined. On the other hand, process (1) has beenwidely investigated for techniques for preparing various shapes and someactual on-site production cases in paper mills have been shown.Especially, calcium carbonate in the form of acicular, columnar orradiating aragonite crystals are known to remarkably improve opacity andbulk when used in paper.

[0008] However, this process produces calcium carbonate as the soleproduct and therefore requires high production costs contrary to users'demands for cost reduction, and the resulting calcium carbonate isunsuitable or limited for use in inexpensive papers.

[0009] A possible alternative is to use, as a material for papermaking,the calcium carbonate generated as a by-product during thecausticization step for recovering/regenerating the digesting agent inthe kraft pulping process.

[0010] In the sulfate or soda pulping process, the wood is digested witha mixed chemical solution of sodium hydroxide and sodium sulfide at hightemperature and high pressure to separatepulp as a solids phase. whilethe chemical solution and other components than pulp dissolved from thewood are recovered as waste pulping liquor (black liquor) andconcentrated and burned. Then, the components dissolved from the woodare recovered as a heat source while inorganic matter in the blackliquor is recovered as sodium carbonate and sodium sulfide and dissolvedin water or a dilute liquor called weak liquor in which are dissolved apart of white liquor components generated by washing the calciumcarbonate sludge from the reaction shown below to give a green liquor.

[0011] This green liquor is mixed with quick lime to produce calciumcarbonate by reactions (1) and (2):

CaO+H₂O→Ca(OH)₂  (1)

Ca(OH)₂+Na₂CO₃→CaCO₃+2NaOH  (2)

[0012] This calcium carbonate can be prepared at very low cost becauseit is a by-product generated in the process for preparing white liquoras a main product. Moreover, it can be expected to improve the kineticsof the above reactions (1) and (2) and the purification of white liquorand to reduce waste, because the removal of calcium carbonate from thecalcium circulating cycle (calcium carbonate, quick lime, slaked lime)in an originally closed system of the causticization step allows theinside of the system to be cleaned and the circulating lime to be highlypurified.

[0013] However, it was difficult to control the shape of calciumcarbonate obtained by the reaction in the conventional process, and thecrystal structure showed irregular or massive calcite crystals in cubic,hexagonal or various other shapes having a large particle size andrather resembled conventional heavy calcium carbonate. Thus, thiscalcium carbonate could not be used as filler to produce normalfine-quality papers or coated papers having sufficient bulk, whiteness,opacity, smoothness, writing suitability, touch, printability or otherproperties. Another serious problem was plastic wire abrasion under therecent trend toward large papermaking machines at high speed.

[0014] Thus, it was difficult to efficiently and inexpensively preparecalcium carbonate, especially in the form of aragonite crystals, as afiller or pigment which shows lower plastic wire abrasion duringpapermaking and which can be used in lower amounts to produce lighterpapers having the same printing quality or at the same ash content toproduce fine-quality papers or coated papers with high bulk and opacityand stiffness.

[0015] In view of the above situation, it is an object of the presentinvention to provide inexpensive calcium carbonate, especially in theform of aragonite crystals, which shows lower plastic wire abrasionduring papermaking and which can be used to produce stiff and highlyopaque fine-quality papers or coated papers having excellent printingqualities or other properties, by taking advantage of the causticizationstep.

SUMMARY OF THE INVENTION

[0016] We previously disclosed an invention on the basis of the findingthat the above problems can be solved by taking advantage of thecausticization step of the sulfate or soda pulping process tocontinuously add the green liquor from the causticization step of thesulfate or soda pulping process to the milk of lime obtained by slakingquick lime containing calcium carbonate at a specific level or less witha liquor having a pH of 5.5-13.5 at controlled loading rate and reactiontemperature (JPA 226974/98). However, this process produces massivecalcite crystals when a weak liquor having a pH of 13.5 or more is usedfor slaking quick lime. Moreover, it was difficult to obtain aragonitecrystals at low concentrations of milk of lime or the loading period hadto be prolonged to maintain a proper shape even at low concentrations ofmilk of lime within a defined range.

[0017] As a result of further careful studies, we accomplished thepresent invention on the basis of the finding that aragonite crystalscan be obtained by taking advantage of the causticization step of thesulfate or soda pulping process to add an aqueous alkaline solutionhaving a hydroxide ion level of 3 mol/l or less and containing 0.25 molor less, preferably 0.1 mol or less of carbonate ion per 1 mol of quicklime to quick lime and/or slaked lime at a quick lime concentration of1-60% by weight with stirring to prepare milk of lime and thencontinuously add green liquor at a controlled loading rate and reactiontemperature. The pH of the aqueous alkaline solution containingcarbonate ion here is preferably more than 13.5. The lower limit of thecarbonate ion level in said aqueous alkaline solution is not definedbecause it is difficult to control such a level due to the variationwith dissolution of carbon dioxide in the air into both aqueous alkalinesolution and water. It was found that acicular, columnar and radiatingcalcium carbonates having a high content of aragonite crystals and acontrolled shape of particles having a minor axis of 0.1-1.5 μm and amajor axis of 0.3-15 μm can be prepared by processes of the presentinvention. They are excellent in whiteness, bulk and opacity as a fillerfor papermakingwith lower wire abrasion. At the same time, they can beprepared at greatly lower cost as compared with calcium carbonateobtained by the conventional process involving the reaction between milkof lime and carbon dioxide. Additionally, the removal of calciumcarbonate from the process shortens or even eliminates kiln operation atsome doses of the causticized light calcium carbonate, thus saving theoverall cost of the causticization step.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a scanning electron microphotograph showing the crystalstructure of radiating calcium carbonate obtained in Example 1.

[0019]FIG. 2 shows the result of X-ray diffraction of the productobtained in Example 1.

[0020]FIG. 3 is a scanning electron microphotograph showing the crystalstructure of columnar calcium carbonate obtained in Example 2.

[0021]FIG. 4 is a scanning electron microphotograph showing the crystalstructure of irregular calcium carbonate obtained in Comparative example3.

[0022]FIG. 5 shows the result of X-ray diffraction of the productobtained in Comparative example 3.

THE MOST PREFERRED EMBODIMENTS OF THE INVENTION

[0023] Quick lime used in the preparation of milk of lime according tothe present invention may be obtained by calcining limestone essentiallyconsisting of calcium carbonate or the calcium carbonate generated whensodium carbonate is converted into sodium hydroxide via thecausitization step of the sulfate or soda pulping process. The calcinerused here may be any apparatus for converting calcium carbonate intoquick lime (calcium oxide) such as Beckenbach kiln, Meltz kiln, rotarykiln, Kunii kiln, KHD kiln, Top-shaped kiln, Calmatic kiln, fluidizedbed calciner, vertical mixer/calciner.

[0024] As to levels of impurities in the resulting calcium carbonate,coloring element levels (Fe, Mn, etc.) are especially critical. However,they can be controlled by appropriately selecting the quick limeobtained from starting limestone having low coloring element levelsaccording to the purpose of the product paper. In the case of the quicklime recalcined in a rotary kiln or fluidized bed calciner or the likevia the causticization step, the amount of the starting limestone havinglow coloring element levels supplied to the calcium circulating cycle ofthe causticization step or the amount of the resulting quick lime aftercalcination can be varied appropriately because coloring element levelsvary with the ratio between calcium carbonate removed from the systemand calcium carbonate recirculating in the system or other factors.

[0025] Slaked lime used in the preparation of milk of lime may beobtained by wet- or dry-slaking said quick lime, but dry-slaked lime ispreferred for the shape of the resulting calcium carbonate.

[0026] The solution to be added for the preparation of milk of lime canbe an aqueous alkaline solution containing 0.25 mol or less, preferably0.1 mol or less of carbonate ion per 1 mol of quick lime. If the aqueousalkaline solution containing carbonate ion used here has a hydroxide ionlevel exceeding 3 mol/l, it is costly and of no practical use due to theimbalance between Na and S in the white liquor produced in the kraftpulping process. Moreover, causticization reaction itself does notreadily proceed. This aqueous alkaline solution may be any alkalinesolution but suitably an aqueous dilution of white liquor producedduring the causticization step or a weak liquor consisting of thesupernatant of solutions cleared of precipitates of green liquor orwhite liquor (dregs, calcium carbonate sludge) in view of the fact thatthis is a process via the causticization step. When further high-qualitycalcium carbonate in the form of aragonite crystals is to be obtained,it is preferable to use an aqueous solution free from carbonate ion suchas an aqueous sodium hydroxide solution. If more than 0.25 mol ofcarbonate ion is contained per 1 mol of quick lime in a solution usingwhite liquor or weak liquor, the resulting calcium carbonate formsspindle-like or massive calcite crystals.

[0027] Milk of lime should be prepared at a quick lime concentration of1-60% by weight. If the lime concentration exceeds 60% by weight, theviscosity of milk of lime becomes too high to practically agitate. Ifthe lime concentration is lower than 1% by weight, however, productivityis low for practical use.

[0028] Mixing for slaking quick lime and suspending the slaked lime maybe performed using a means appropriately selected from conventionalextruders, kneaders and blenders equipped with agitating blades or apump to suit the viscosity of the liquor or slurry during mixing (seeHandbook of Chemical Engineering published by Maruzen, Mar. 18, 1988).

[0029] Green liquor used in the causticization reaction according to thepresent invention can be green liquor generated from the causticizationstep of the conventional sulfate or soda process. If furtherhigh-quality calcium carbonate is to be obtained, it is preferable touse sodium carbonate crystallized by cooling or heating green liquor toconcentration and diluted or not in water or weak liquor. When solidsodium carbonate is used, it may be appropriately added. When an aqueoussodium carbonate solution is used, it should be used at an Na₂CO₃concentration of 20-230 g/L (as Na₂O, the same basis as below),preferably 60-180 g/L, more preferably 80-120 g/L. If the Na₂CO₃concentration is lower than 20 g/L, the final concentration of whiteliquor is lowered and should be modified before it is used fordigestion. However, a solution having a concentration higher than 230g/L cannot be prepared because the saturation concentration isapproached.

[0030] Said milk of lime and green liquor should be mixed at a loadingrate of 0.002-0.12 g sodium carbonate/min/g quick lime, preferably0.002-0.04 g/min/g. If the loading rate is lower than 0.002 g sodiumcarbonate/min/g, productivity is low for practical use. If the loadingrate is higher than 0.12 g/min/g, however, massive calcite crystals areformed with higher wire abrasion.

[0031] Causticization reaction should be carried out at a reactiontemperature of 30-105° C., preferably 40-90° C. Temperatures higher than105° C. are uneconomic because a pressure-type causticization system orthe like is needed over the boiling point at atmospheric pressure.However, temperatures lower than 30° C. are also unsuitable becausearagonite crystals are scarcely formed and system modifications arerequired to cool green liquor of about 80° C., thereby adding costs.

[0032] Agitation during causticization reaction may be performed using ameans appropriately selected from conventional extruders, kneaders andblenders equipped with agitating blades or a pump that are suitable forhomogeneously mixing the milk of lime prepared by slaking quick lime andsuspending the slaked lime with sodium carbonate (see Handbook ofChemical Engineering published by Maruzen, Mar. 18, 1988).

[0033] Under the conditions described above, acicular, columnar orradiating calcium carbonate consisting of particles having a minor axisof 0.1-1.5 μm and a major axis of 0.3-15 μm can be prepared.

[0034] As compared with calcium carbonate previously obtained via thecausticization step, calcium carbonate in the form of aragonite crystalsobtained by the present invention shows lower wire abrasion and can beused to produce fine-quality papers or coated papers having excellentstiffness, whiteness, opacity, smoothness, writing suitability, touch,printability or other properties. From this it can be readily inferredthat it can be used in newspapers, medium papers, printing papers, bookpapers, bill papers, dictionary papers, double-side ground wood kraftpapers, bleached kraft papers, tissue papers, rice papers, Indianpapers, paper boards, non-carbon papers, art papers, light coatedpapers, cast coated papers, wall papers, heat-sensitive papers or thelike to give them excellent properties such as stiffness, whiteness,opacity, smoothness, writing suitability, touch, printability or thelike. It also can be used in various pigments to give excellent gloss,smoothness, printability, and like properties. In addition to papers, itcan also be used in rubbers, plastics, paints, sealing agents,adhesives, fertilizers, etc.

EFFECTS OF THE INVENTION

[0035] Although the mechanism of the present invention is not completelyunderstood, it is thought that aragonite crystals may readilyprecipitate in the reaction between quick lime/slaked lime and sodiumcarbonate in the presence of an alkali. However, calcite crystals arelikely to be produced if carbonate ions excessively exist in thesolution during this reaction. Thus, the proportion of aragonitecrystals tends to be lowered if sodium carbonate is excessive during thepreparation of milk of lime or if the loading rate of green liquor isincreased during the reaction.

[0036] This calcium carbonate mainly has three features. Firstly, itimproves plastic wire abrasion during high-speed papermaking. Secondly,it can be used as a filler to improve bulk, opacity, whiteness andstiffness. Thirdly, it improves gloss after printing and surfacestrength when it is ground and used as a pigment. The first featureresults from the acicular primary particles with high aspect ratio andlittle sharp edges which are advantageous for improving abrasion becauseof the low frictional resistance during contact with wire. The secondfeature is explained by electron microscopy of the surface/section ofthe resulting paper, which shows that acicular calcium carbonateparticles fill gaps between pulp fibers as if they are microfibers andthey are stiff enough to form many minute air spaces so as to rendergood bulk, opacity and whiteness. The third feature results from theacicular, columnar or radiating particles of 0.3-15 μm before grinding,which renders low gloss and improved ink absorption. It is thought thatprintabilities such as glossiness after printing or the like areimproved because the particles have a relatively homogeneous size aftergrinding.

[0037] The following examples illustrate the present invention ascompared with comparative examples without, however, limiting the samethereto as a matter of course.

EXAMPLES

[0038] Test Methods

[0039] (1) Alkalinity was determined according to TAPPI 624 hm-85,TAPPI625 hm-85 or similar methods.

[0040] (2) Average particle size of light calcium carbonate wasdetermined with a laser diffraction-type particle size distributionanalyzer (Cirrus model 715) after the product was washed with water,filtered, and diluted with water.

[0041] (3) Morphology was observed with a scanning electron microscope(JSM-5300 from JEOL Ltd.) after the product was washed with water,filtered and dried. On the basis of this observation, the minor andmajor axes of 30 particles were measured.

[0042] (4) Crystal structure was determined with an X-ray diffractometerRAD-2C from Rigaku.

[0043] (5) Wire abrasion was determined as follows.

[0044] Tester: Nippon Filcon wire wear tester.

[0045] Measurement conditions: slurry concentration 0.5%, flow rate 0.65L/min, a ceramic roll having a diameter of 60 φ rotated at 1500 rpm,contact angle 111 degree, weight 1.25 kg, wire type COS60 of 40×140 mm,testing period 90 min. ${{Abrasion}\quad (\%)} = {\frac{\begin{matrix}\left\lbrack {{{Wire}\quad {weight}\quad {before}\quad {testing}\quad (g)} -} \right. \\\left. {{Wire}\quad {weight}\quad {after}\quad {testing}\quad (g)} \right\rbrack\end{matrix}}{{Wire}\quad {weight}\quad {before}\quad {testing}\quad (g)} \times 100}$

Example 1

[0046] In a four-necked flask having a suitable capacity (the samevessel was used in the example and comparative examples below), slakedlime was mixed with a 7-fold dilution of white liquor in water(NaOH:Na₂CO₃:Na₂S=0.17:0.04:0.06 mol/l) at a quick lime concentration of10% by weight to prepare milk of lime, which was then causticized withgreen liquor (Na₂CO₃:Na₂S=1.6:0.5 mol/l; the same composition as below)under the conditions of a sodium carbonate loading rate of 0.04 g(sodium carbonate)/min/g (quick lime), a temperature of 50° C. and anagitation speed of 400 rpm (using KYOEI POWER STIRRER TYPE PS-2N; thesame agitator as below). The product was found to be calcium carbonatein the form of radiating aragonite crystals having an average particlesize of 5.6 μm in which primary particles had an average major axis of2.1 μm and an average minor axis of 0.3 μm. The wire abrasion was 0.2%.Experimental conditions and results are shown in Table 1.

Example 2

[0047] The procedure of Example 1 was repeated except that a 2-folddilution of white liquor in water (NaOH:Na₂CO₃:Na₂S=0.60:0.14:0.21mol/l) was used at a quick lime concentration of 40% by weight toprepare milk of lime, which was then causticized with green liquor underthe conditions of a sodium carbonate loading rate of 0.005 g/min/g and atemperature of 90° C. The product was found to be calcium carbonate inthe form of columnar aragonite crystals having an average particle sizeof 7.0 μm in which primary particles had an average major axis of 6.5 μmand an average minor axis of 0.6 μm. The wire abrasion was 0.1%.Experimental conditions and results are shown in Table 1.

Comparative Example 1

[0048] The procedure of Example 1 was repeated except that an aqueous 1mol/l NaOH solution containing 0.8 mol/l Na₂CO₃ was used to prepare milkof lime. The reaction product was found to be spindle-like calciumcarbonate having an average particle size of 3.6 μm in which primaryparticles had an average major axis of 2.8 μm and an average minor axisof 0.5 μm. The wire abrasion was 0.3%. Experimental conditions andresults are shown in Table 1.

Comparative Example 2

[0049] The procedure of Example 2 was repeated except that the sodiumcarbonate loading rate was 2 g/min/g. The reaction product was found tobe calcium carbonate consisting of irregular primary particles having anaverage particle size of 5.6 μm. The wire abrasion was 1.0%.Experimental conditions and results are shown in Table 1.

Comparative Example 3

[0050] The procedure of Example 1 was repeated except that thecausticization temperature was 20° C. The reaction product was found tobe calcium carbonate consisting of irregular primary particles having anaverage particle size of 6.2 μm. The wire abrasion was 1.3%.Experimental conditions and results are shown in Table 1. TABLE 1Examples Comparative examples 1 2 1 2 3 Concentration of milk 10 40 1010 10 of lime (%) Composition of slaking/ dispersing solvent NaOH(mol/L) 0.17 0.60 1.00 0.17 1.00 Na₂CO₃ (mol/L) 0.04 0.14 0.80 0.04 0.00Na₂S (mol/L) 0.06 0.21 0.00 0.06 0.00 Sodium carbonate source greengreen green green green liquor liquor liquor liquor liquor Sodiumcarbonate loading rate 0.04 0.005 0.002 2 0.002 (g as Na₂CO₃/min/g asCaO) Temperature (° C.) 50 90 50 50 20 Particle shape radiating columnarspindle-like massive massive Average particle size (μm) 5.6 7.0 3.6 5.66.2 Major axis (μm) 2.1 6.5 2.8 — — Minor axis (μm) 0.3 0.6 0.5 — — Wireabrasion (%) 0.2 0.1 0.3 1.0 1.3 Crystal structure aragonite aragonitecalcite calcite calcite

[0051] As shown in Examples 1 to 2, calcium carbonates according to thepresent invention were in the form of acicular, columnar or radiatingaragonite crystals. They showed lower plastic wire abrasion. Moreover,processes of the present invention are able to greatly reduce productioncosts because these calcium carbonates could be prepared by takingadvantage of the conventional causticization step. According to thepresent invention, the loading period of green liquor can also bereduced and aragonite can be prepared even at low concentrations of milkof lime to increase the content of aragonite in the resulting calciumcarbonate. In addition, the use of diluted white liquor for thepreparation of milk of lime reduces the amount of water used to preparemilk of lime as compared with the process disclosed in JPA 226974/98,thus limiting any loss in alkali concentration in white liquor after thecausticization step.

1. A process for producing calcium carbonate in the form of aragonitecrystals which is useful as a filler for papermaking via thecausticization step of the sulfate or soda pulping process, comprisingadding an aqueous alkaline solution having a hydroxide ion level of 3mol/l or less and containing 0.25 mol or less, preferably 0.1 mol orless of carbonate ion per 1 mol of quick lime to quick lime and/orslaked lime at a quick lime concentration of 1-60% by weight withstirring to prepare milk of lime, and then adding green liquor to saidmilk of liquor at a loading rate of 0.002-0.12 g (sodiumcarbonate)/min/g (quick lime) to perform a causticization reaction at atemperature of 30-105° C., preferably 40-90° C.
 2. The process of claim1 wherein said aqueous alkaline solution has a pH higher than 13.5. 3.Calcium carbonate produced by the process of claim 1, which is useful asa filler for papermaking or a coating pigment for coated papers.
 4. Acoating composition using the calcium carbonate of claim 3 as a coatingpigment.
 5. A paper using the calcium carbonate of claim 3 as a fillerfor papermaking or a coated paper using the calcium carbonate of claim 3as a coating pigment.